Oil sorbent devices are very well known in the art. They come in shapes of sheets, sweeps, blankets, pads, pillows, mats, etc., in many different sizes. Rather thin (normally no thicker than ½ inch) nonwoven polypropylene or cotton sheets, sweeps, blankets, pads are commonly used for collection of oil on solid surfaces and water, and widely described in the suppliers brochures and literature (e.g. The Basics of Oil Spill Cleanup by Mery Fingas, The Second Edition, pp. 105-106).
Major advantages of these sheets include the ease of the use and the short time need to completely fill the volume of the sheet with the absorbed liquid. The high efficiency of oil sorption of these types of sheets is due to the fact that they are relatively thin and light. These types of sheets, when placed on water covered by oil, do not sink into the water, but rather their bottom surfaces tend to lie on the top of the oil film so that penetration of the oil into the sheet is through the bottom surface of the sheet and takes place fairly quickly. When placed on a thin oil layer on water, the pad absorbs the oil through its bottom surface so that further oil penetration occurs very slowly through its edges after it has sunk down a little. Further disadvantages of these types of oil absorption devices are their rather small volume (because of the small thickness) and accordingly a small potential amount of absorbed oil, and relatively high price of nonwovens, which results in high cost of oil retrieval. Besides, being very light these pads may be blown and drifted away by wind and water stream.
Another type of the sorbent devices of this kind are pads having porous flexible casing filled with oil sorbent material, and described in the U.S. Pat. No. 5,186,831 and U.S. Pat. No. 5,407,575. These pads are thicker than the nonwoven sorbent sheets and accordingly have higher volume, and therefore greater oil sorption potential. The sorbent fillers in these pads are less expensive than material of sorbent nonwoven pads, which means lower price per the weight unit of the device, and theoretically less oil retrieval cost. However, the pads disclosed in these publications exhibit low oil sorption efficiency. The problem stems from the fact that the pads are quite thick and relatively heavy, with low surface areas so that when placed on oil on a body of water the pads sink lower into the water causing oil to be displaced from under the bottom of the pad with the oil contacting the pad around its edges resulting in the oil penetrating into the pad through a very small area on the pad edges.
Another known oil absorbent pad are quilted pads having top and bottom surfaces of a flexible casing filled with oil absorbent material with the top and bottom stitched together at different positions to provide a pad with the oil absorbent material confined so that it does not move around and bunch up between the top and bottom casing material. A disadvantage of these quilted pads is that by stitching the top and bottom materials together in period locations this produce pockets with convex downward bottom blocks. In the case of oil on water it translates into much deeper submersion of these quilted pads into water in comparison with flat pads of the same size and weight. If the depth of penetration of the quilted pads into water is larger than the oil layer thickness, oil sorption goes only through lines of oil contact with side surfaces of the quilted blocks.